clc;
syms x y z;
f=x^2+x*y+y^2-3;
F1=impldiff(f,x,y,1);
f2=impldiff(f,x,y,2)F2=subs(f2,x^2+x*y+y^2,3)
f3=impldiff(f,x,y,3);F3=subs(f3,x^2+x*y+y^2,3)
f4=impldiff(f,x,y,4);F4=subs(f4,x^2+x*y+y^2,3)%将x^2+x*y+y^2替换为3